Is it normal for a newly adopted dog to limit food intake?

We adopted a five year-old chihuahua this past Saturday from a local shelter. He seems very well adjusted (sits on our laps all the time, walks well when we take him out for walks and bathroom times, has no problem staying in his crate at night or when we go out, etc); however, he won't really eat the food we put out. He might eat a piece or two from our hands, but he won't go over to the bowl to eat (unless I mix wet food with the dry food). He ate dry food at the shelter, so it shouldn't be a wet/dry thing. We bought Nutro Ultra food for him, so maybe he's just used to eating the crappy food with all the corn filler and byproducts in it? Any ideas on what to do? He's only a five pound dog, so the fact that he isn't really eating makes me nervous. Then again, he's only been here for about 48 hours, so maybe it'll just take a little time. Any advice is appreciated!